CVE-2026-9803 MEDIUM

CVE-2026-9803: Keycloak: keycloak: denial of service via malformed authorization header

Vendor Red Hat
Product Red Hat build of Keycloak 26.6.3
Weakness CWE-125
Published May 28, 2026
Last update June 10, 2026
View on NVD All CVEs

CVSS base score

5.3/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality None
Integrity None

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

What the vulnerability does

01Description

A flaw was found in Keycloak's ClientRegistrationAuth component. A remote unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with a malformed 'Authorization: Bearer' header to any client registration endpoint. This can lead to an ArrayIndexOutOfBoundsException, causing the server to return an HTTP 500 error and resulting in a Denial of Service (DoS) for the affected service.

Key dates

02Disclosure timeline

May 28, 2026 CVE published
June 10, 2026 Record updated